Cam oiling query

[Turn & Burn]

I’m currently stripping and modifying my N42 block ready for reboring, perf cam etc. In the Honsowetz book ‘How Tune your Nissan engine’ it talks about opening up the restriction orifice in the top of the block from 2mm to 3mm to increase flow to the cam, especially relevant with a high lift cam without a spray bar fitted. The orifice is located centrally in the rh side of the block top. There is a photo and a diagram that show this.
My block has two orifices fitted, as shown in the photo (washers placed on them for clarity), and this second orifice is not mentioned. As far as I can tell this leads to the cam carriers, so I already have twice the flow to the cam.
I assume others have come across this 2nd orifice? Have u opened them both up or left as is? I can’t find any mention on the internet. Just for info I have a turbo oil pump for the new build.
Cheers

 

[jonbills]

I have a vague recollection I investigated that once and came to the conclusion only the central one is supply to the cam, but can't remember why.
I didn't open mine up. Again, can't remember why. Maybe put off by stories of bottom end starvation on RB engines after similar shenanigans. Or the engine builder advised against it. Or 5/40 oil flows plenty anyway. Anyway, the cam has plenty lift and is doing fine. No damage after 3 years of abuse.

 

[jonbills]

I think I remember... I reckon the hole at the front of the head is the supply TO the timing chain oiler in the block.

 

[Turn & Burn]

Thanks for the replies, I’ll go back and have another look, it makes sense for it to feed the chain.

 

[Albrecht]

A bit small, but hopefully this is legible:

 

[Turn & Burn]

Really good info, thanks. So post ‘77 there were 2 feeds to the cam.
Any thoughts on whether it’s worth expanding these at all? The larger capacity oil pump should still be capable of supporting an increase in flow but Jon seems to have managed fine without. Pmac??

 

[Albrecht]

Really good info, thanks. So post ‘77 there were 2 feeds to the cam.
Any thoughts on whether it’s worth expanding these at all?

My gurus have always recommended going up very slightly in size. Not too much. 1mm or so should be enough.

 

[Turn & Burn]

Thanks for that, I think I’ll go up to 3mm on central orifice only then.


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